In this paper, elastic wave scattering from rough surfaces and rough cracks is investigated theoretically. Two approaches based on the reciprocity relation a re developed. In one of them, the s cattering coefficient is expressed in terms of the normal stress on a reference surface in the presence o f the roughness and is approximated by an equivalent boundary condition in terms of the first order perturbation in stress field (Brekhovskikh's boundary condition). In the other, t he formulation is performed in terms of the velocity d istribution on rough surface and various approximation t echniques are discussed. The results are compared and examples are given. X